Kieron Freeman's late goal kept Sheffield United's promotion charge on track with a 1-0 win over Northampton.Freeman struck just a minute from time to finally end Northampton's resistance and send the Blades top of Sky Bet League One, at least temporarily.United's Paul Coutts had a low drive saved by Adam Smith early on while Northampton's first effort came from Sam Hoskins, whose shot from inside the area was charged down.The home side then enjoyed a good spell with Freeman firing in a shot which was deflected off target.Billy Sharp also missed the target with a header and Coutts shot narrowly wide.After Paul Anderson headed wide at the other end, United threatened again when Mark Duffy's free-kick was deflected wide. Duffy also had a shot easily saved.Sharp went close to scoring midway through the second half when his effort hit a post while Matthew Taylor also threatened for the visitors with a free-kick which was saved by Simon Moore.Freeman, though, scored the winner when he fired into the roof of the net from close range to send United above Scunthorpe.